TECHNICAL SPECIFICATION

Transcription

1 IEC/TS TECHNICAL SPECIFICATION Edition Selection and dimensioning of high-voltage insulators intended for use in polluted conditions Part 2: Ceramic and glass insulators for a.c. systems IEC/TS :2008(E)

2 THIS PUBLICATION IS COPYRIGHT PROTECTED Copyright 2008 IEC, Geneva, Switzerland All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or your local IEC member National Committee for further information. Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie et les microfilms, sans l'accord écrit de la CEI ou du Comité national de la CEI du pays du demandeur. Si vous avez des questions sur le copyright de la CEI ou si vous désirez obtenir des droits supplémentaires sur cette publication, utilisez les coordonnées ci-après ou contactez le Comité national de la CEI de votre pays de résidence. IEC Central Office 3, rue de Varembé CH-1211 Geneva 20 Switzerland inmail@iec.ch Web: About IEC publications The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the latest edition, a corrigenda or an amendment might have been published. Catalogue of IEC publications: The IEC on-line Catalogue enables you to search by a variety of criteria (reference number, text, technical committee, ). It also gives information on projects, withdrawn and replaced publications. IEC Just Published: Stay up to date on all new IEC publications. Just Published details twice a month all new publications released. Available on-line and also by . Electropedia: The world's leading online dictionary of electronic and electrical terms containing more than terms and definitions in English and French, with equivalent terms in additional languages. Also known as the International Electrotechnical Vocabulary online. Customer Service Centre: If you wish to give us your feedback on this publication or need further assistance, please visit the Customer Service Centre FAQ or contact us: csc@iec.ch Tel.: Fax:

3 IEC/TS TECHNICAL SPECIFICATION Edition Selection and dimensioning of high-voltage insulators intended for use in polluted conditions Part 2: Ceramic and glass insulators for a.c. systems INTERNATIONAL ELECTROTECHNICAL COMMISSION PRICE CODE S ICS ISBN Registered trademark of the International Electrotechnical Commission

4 2 TS IEC:2008(E) CONTENTS FOREWORD Scope and object Normative references Terms, definitions and abbreviations Terms and definitions Abbreviations Principles Materials Site severity determination Determination of the reference unified specific creepage distance (RUSCD) Choice of profile General recommendations for porcelain and glass profiles Profile suitability Checking the profile parameters Alternating sheds and shed overhang Spacing versus shed overhang Minimum distance between sheds Creepage distance versus clearance Shed angle Creepage factor Correction of the RUSCD Correction for altitude K a Correction for insulator diameter K ad Determination of the required minimum nominal creepage distance Confirmation by testing Determination of the long-duration withstand voltage Selection of the standard pollution withstand test type Artificial pollution test parameters Criteria of confirmation...21 Bibliography...22 Figure 1 RUSCD as a function of SPS class...9 Figure 2 Typical standard profiles...10 Figure 3 Typical open profiles...11 Figure 4 Typical anti-fog profiles...11 Figure 5 Typical alternating profiles...11 Figure 6 Typical pin insulator shed profiles...12 Figure 7 K ad as a function of insulator diameter...18

5 TS IEC:2008(E) 3 Table 1 Principal advantages (+) and disadvantages (-) of main profile types...10 Table 2 Profile suitability, relative to a standard profile, for porcelain and glass insulators assuming the same creepage distance per unit or string...13 Table 3 Profile suitability, relative to a standard profile, for porcelain and glass insulators assuming the same insulating length...14 Table 4 Artificial pollution test parameters for confirmation by testing...20

6 4 TS IEC:2008(E) INTERNATIONAL ELECTROTECHNICAL COMMISSION SELECTION AND DIMENSIONING OF HIGH-VOLTAGE INSULATORS INTENDED FOR USE IN POLLUTED CONDITIONS Part 2: Ceramic and glass insulators for a.c. systems FOREWORD 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as IEC Publication(s) ). Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and nongovernmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations. 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested IEC National Committees. 3) IEC Publications have the form of recommendations for international use and are accepted by IEC National Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any misinterpretation by any end user. 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications transparently to the maximum extent possible in their national and regional publications. Any divergence between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter. 5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any equipment declared to be in conformity with an IEC Publication. 6) All users should ensure that they have the latest edition of this publication. 7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and members of its technical committees and IEC National Committees for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications. 8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is indispensable for the correct application of this publication. 9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent rights. IEC shall not be held responsible for identifying any or all such patent rights. The main task of IEC technical committees is to prepare International Standards. In exceptional circumstances, a technical committee may propose the publication of a technical specification when the required support cannot be obtained for the publication of an International Standard, despite repeated efforts, or the subject is still under technical development or where, for any other reason, there is the future but no immediate possibility of an agreement on an International Standard. Technical specifications are subject to review within three years of publication to decide whether they can be transformed into International Standards. IEC/TS , which is a technical specification, has been prepared by technical committee 36: Insulators. This first edition of IEC/TS , together with IEC/TS , cancels and replaces IEC/TR 60815, which was issued as a technical report in It constitutes a technical

7 TS IEC:2008(E) 5 revision and now has the status of a technical specification. The text of this technical specification is based on the following documents: Enquiry draft 36/265/DTS Report on voting 36/271A/RVC Full information on the voting for the approval of this technical specification can be found in the report on voting indicated in the above table. This publication has been drafted in accordance with the ISO/IEC Directives, Part 2 A list of all the parts in the future IEC series, under the general title Selection and dimensioning of high-voltage insulators intended for use in polluted conditions, can be found on the IEC website. The committee has decided that the contents of this publication will remain unchanged until the maintenance result date indicated on the IEC web site under " in the data related to the specific publication. At this date, the publication will be transformed into an International standard, reconfirmed, withdrawn, replaced by a revised edition, or amended. A bilingual version of this publication may be issued at a later date.

8 6 TS IEC:2008(E) SELECTION AND DIMENSIONING OF HIGH-VOLTAGE INSULATORS INTENDED FOR USE IN POLLUTED CONDITIONS Part 2: Ceramic and glass insulators for a.c. systems 1 Scope and object IEC/TS , which is a technical specification, is applicable to the selection of ceramic and glass insulators for a.c. systems, and the determination of their relevant dimensions, to be used in high-voltage systems with respect to pollution. This part of IEC gives specific guidelines and principles to arrive at an informed judgement on the probable behaviour of a given insulator in certain pollution environments. The basis for the structure and approach of this part of IEC is fully explained in IEC/TS The object of this technical specification is to give the user means to: determine the reference unified specific creepage distance (RUSCD) from site pollution severity (SPS) class; evaluate the suitability of different insulator profiles; determine the necessary USCD by applying corrections for insulator shape, size, position, etc. to the RUSCD; if required, determine the appropriate test methods and parameters to verify the performance of the selected insulators. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC , International Electrotechnical Vocabulary Part 471: Insulators IEC 60507, Artificial pollution tests on high-voltage insulators to be used on a.c. systems IEC/TS , Selection and dimensioning of high-voltage insulators for polluted conditions Part 1: Definitions information and general principles 3 Terms, definitions and abbreviations For the purposes of this document, the following terms, definitions and abbreviations apply. The definitions given below are those which either do not appear in IEC or differ from those given in IEC

9 TS IEC:2008(E) Terms and definitions 3.2 unified specific creepage distance USCD creepage distance of an insulator divided by the r.m.s. value of the highest operating voltage across the insulator NOTE 1 This definition differs from that of specific creepage distance where the line-to-line value of the highest voltage for the equipment is used (for a.c. systems usually U m / 3). For line-to-earth insulation, this definition will result in a value that is 3 times that given by the definition of specific creepage distance in IEC/TR (1986). NOTE 2 For U m see IEV [1] 1. NOTE 3 It is generally expressed in mm/kv and usually expressed as a minimum. 3.3 reference unified specific creepage distance RUSCD initial value of unified specific creepage distance for a pollution site before correction for size, profile, mounting position, etc. according to this technical specification and generally expressed in mm/kv 3.4 Abbreviations CF creepage factor ESDD equivalent salt deposit density NSDD non soluble deposit density SDD salt deposit density SES site equivalent salinity SPS site pollution severity USCD unified specific creepage distance RUSCD reference unified specific creepage distance 4 Principles The overall process of insulation selection and dimensioning can be summarized as follows: Firstly, using IEC/TS : determine the appropriate approach: 1, 2 or 3 as a function of available knowledge, time and resources; collect the necessary input data, notably system voltage, insulation application type (line, post, bushing, etc.); collect the necessary environmental data, notably site pollution severity and class. At this stage, a preliminary choice of possible candidate insulators suitable for the applications and environment may be made. Then, using this technical specification: refine the choice of possible candidate ceramic or glass insulators suitable for the environment; 1 References in square brackets refer to the bibliography.

10 8 TS IEC:2008(E) determine the reference USCD for the insulator types and materials, either using the indications given in this technical specification, or from service or test station experience in the case of approach 1 (Clause 7); choose suitable profiles for the type of environment (Clause 8); verify that the profile satisfies certain parameters, with correction or action according to the degree of deviation (Clause 9); modify, where necessary (approaches 2 and 3), of the RUSCD by factors depending on the size, profile, orientation, etc. of the candidate insulator (Clauses 10 and 11); verify that the resulting candidate insulators satisfy the other system and line requirements such as those given in Table 2 of IEC/TS (e.g. imposed geometry, dimensions, economics); verify the dimensioning, if required in the case of approach 2, by laboratory tests (see Clause 12). NOTE Without sufficient time and resources (i.e. using approach 3), the determination of the necessary USCD will have less accuracy. 5 Materials This technical specification is applicable to ceramic and glass insulators. The guidance given here assumes that the insulators are of standard manufacture without any surface modification or treatment. Technologies exist intended to improve the performance of such insulators under pollution, for example, semi-conducting glaze and hydrophobic coatings. At present it is not possible to give specific information on the degree and durability of the improvement given by such technologies. As far as the relative performance of ceramic and glass insulators under pollution is concerned, there is no notable consistent difference between these materials; hence the choice of either glass or ceramic material with respect to the other depends purely on factors (e.g. ageing, operating experience, maintenance procedures) which are out of the scope of this technical specification. 6 Site severity determination For the purposes of standardization, five classes of pollution characterizing the site severity are qualitatively defined in IEC/TS , from very light pollution to very heavy pollution, as follows: a Very light; b Light; c Medium; d Heavy; e Very heavy. NOTE These letter classes do not correspond directly to the previous number classes of IEC/TR 60815:1986. The SPS class for the site is determined according to IEC/TS and is used to determine the reference USCD for glass and ceramic insulators. 7 Determination of the reference unified specific creepage distance (RUSCD) Figure 1 shows the relation between SPS class and RUSCD for glass and ceramic insulators. The bars are preferred values representative of a minimum requirement for each class and

11 TS IEC:2008(E) 9 are given for use with approach 3 as described in IEC/TS If the estimation of SPS class tends towards the neighbouring higher class, then the curve may be followed. If exact SPS measurements are available (approach 1 or 2), it is recommended to take a RUSCD which corresponds to the position of the SPS measurements within the class by following the curve in Figure 1. Basic USCD (mm/kv) 60,0 55,0 50,0 45,0 40,0 35,0 30,0 25,0 20,0 22,0 27,8 34,7 43,3 53,7 a b c d e SPS Class IEC 1967/08 Figure 1 RUSCD as a function of SPS class In cases of exceptionally high SPS in, or beyond, class e (see IEC/TS , 8.2) the minimum RUSCD may not be adequate. Depending on service experience and/or laboratory test results a higher USCD can be used; in some instances mitigation may be useful (see IEC/TS , 9.5.5). NOTE It is assumed that the final USCD resulting from the application of the corrections given hereafter to the RUSCD will not correspond exactly to a creepage distance available for catalogue insulators. Hence it is preferred to work with exact figures and to round up to an appropriate value at the end of the correction process. 8 Choice of profile 8.1 General recommendations for porcelain and glass profiles Table 1 below shows a brief summary of the principal advantages and disadvantages of the main profile types with respect to pollution performance. For standard profiles see Figure 2. NOTE In the case of long rods, posts and hollows, the typical standard profile shed inclinations are for the shed top angle α and 8 16 for the shed bottom angle β (illustrated in Figure 2b). Smaller angles are generally considered as being aerodynamic, while larger angles are considered as being anti-fog.